• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.78-81
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• 2008

A numerical study of the unsteady flow in an over-expanded thrust optimized contour and compressed truncated perfect rocket nozzle is carried out in present paper. These rocket nozzles are subject to flow separation in transient phase at engine start-up and/or engine shut-down. The separation flow structures at different pressure ratios are observed. The start-up process exhibits two different shock structures such as FSS (Free Shock Separation) and RSS (Restricted Shock Separation). For a range of pressure ratios, hysteresis phenomenon occurs between these two separation patterns. A three-dimension compressible Navier-Stokes solver is used for the present study. One equation Spalart-Allmaras turbulence model is selected. The computed nozzle wall pressures show a good agreement with the experimental measurements. Present results have shown that present code can be used for the analysis of the transient flows in nozzle.

• International Journal of Fluid Machinery and Systems
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• v.10 no.1
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• pp.86-98
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• 2017

In order to obtain high efficiency and low resistance droplet separation apparatus, axial vane type gas-liquid separators with different guide vanes were designed, and the RNG $k-{\varepsilon}$ model as well as discrete phase model (DPM) were used to investigate the flow pattern inside the separators. It was shown that the tangential velocity distribution under different guide vanes have Rankine vortex characteristics, pressure distribution exhibits a high similarity which value becomes big as the increase of the blade outlet angle and the decrease of the guide vane numbers. The increase of the guide vane numbers and the decrease of the blade outlet angle could make separation improve significantly. The separation efficiency is almost 100% when the droplet diameter is bigger than $40{\mu}m$.

• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.4
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• pp.344-351
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• 2023

Static ejection tests were conducted using the 2,000lb-Class Store to provide ejector model for the store separation simulation. In this study, static ejection test device for 2,000lb-class store was constructed and reaction force applied to store was measured over time. In addition, the trajectories of the ejected store were obtained using photogrammetry and compared with the simulations using developed ejector model. The results of the static ejection test were analyzed to determine the cartridge-orifice combination to be used for store separation. Flight tests were performed by applying the analysis results and verified that the store was safely separated from the aircraft.

• 제어로봇시스템학회:학술대회논문집
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• 1989.10a
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• pp.372-376
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• 1989

One of the major difficulties with modular approach model of separation process simulation is initial guess problem. Only accurate initial guess make the problem converge and large computer memory and calculating time are required. In this study, we use the initial bottom guess value same as given feed condition and update the value the .theta.method. So we examine;(1)the problem converges using initial guess with large range, (2)computer memory and calculating time are reduced considerably.

• Proceedings of the Membrane Society of Korea Conference
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• 2004.05a
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• pp.152-154
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• 2004

A new model of selectively preferential sorption-facilitated transport with fixed site carriers was advanced in this paper. A number of experiments were arranged to demonstrate the ideal above. Preliminary results were obtained from the experiments, and shown the model was applicable for many membrane processes, such as RO, ED, gas separation and liquid membranes etc.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2868-2872
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• 2007

In this study, a passive control using a boat-tail device is conducted for a three-dimensional car model in ground proximity. We consider various boat-tails and investigate the mechanism of drag reduction by them. By varying the length and slant angle of boat-tail, we obtain drag reductions up to 40%. From the oil-surface flow visualization and hot-wire measurement, the drag reduction by the boat-tail is characterized by the shear-layer instability and reattachment on the boat-tail, forming a small separation bubble at the upstream part of boat-tail surface, resulting in the delay of main separation and drag reduction. At high slant angles, the flow fully separates and drag is nearly same as that of no control.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.9
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• pp.1051-1059
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• 1992

In this paper, two general methods using time-series analysis in the functional separation of the myoelectric signal of human arm movements are developed. Autocorrelation, covariance method and sequential least squares algorithm were used to determine the model parameters and the order of signal model to describe six arm movement patterns` the forearm flexion and extension, the wrist pronation and supination, rotation-in and rotation-out. The confidence interval to classify the functions of arm movement was defined by the mean and standard deviation of total squared error. With the error signals of autoregressive(AR) model, the result showed that the highest success rate was obtained in the case of 4th order, and success rate was decreased with increase of order. Autocorrelation was the method of choice for better success rate. This technique might be applied to biomedical and rehabilitation engineering.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.420-427
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• 2011

In this study, numerical simulations of transonic aircraft configurations are performed with various turbulence models and the effect of turbulence models on flow separation are examined. A three-dimensional RANS code and three turbulence models are used for the study. The turbulence models incorporated to the code include Menter's ${\kappa}-{\omega}$ model, Coakley's $q-{\omega}$, and Huang and Coakley's ${\kappa}-{\omega}$, model. Using the code, numerical simulations of DLR-F6 configurations obtained from AIAA CFD Drag Prediction Workshop are conducted. Flow separations on the wing-body juncture and the wing lower surface near pylon are observed. and flow features of the regions are compared with experimental data and other numerical results.

• Korea-Australia Rheology Journal
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• v.12 no.1
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• pp.77-81
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• 2000

Rheological behavior of thermoset/thermoplastic blends of epoxy/polyethersulphone (PES) was monitored during curing of the epoxy resin. During the isothermal curing of the mixture, a fluctuation in viscosity just before the abrupt viscosity increase was observed. This fluctuation is found to be due to the phase separation of PES from the matrix epoxy resin during the curing. The experimentally observed viscosity fluctuation is simulated with a simple two phase suspension model in terms of the increase in domain size. The viscosity profiles obtained experimentally at different isothermal curing temperatures are in good agreement with the predictions from the simple model taking into account the viscosity change due to the growth of PES domain and the network formation of the epoxy matrix.

• Journal of Korea Society of Digital Industry and Information Management
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• v.15 no.3
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• pp.101-109
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• 2019

In addition to enabling access, database accounts play a protective role by defending the database from external attacks. However, because only a single account is used in the database, the account becomes the subject of vulnerability attacks. This common practice is due to the lack of database support, large numbers of users, and row-based database permissions. Therefore if the logic of the application is wrong or vulnerable, there is a risk of exposing the entire database. In this paper, we propose a Least-Privilege Account Separation Model (LPASM) that serves as an information guardian to protect the database from attacks. We separate database accounts depending on the role of application services. This model can protect the database from malicious attacks and prevent damage caused by privilege escalation by an attacker. We classify the account control policies into four categories and propose detailed roles and operating plans for each account.